The individual contribution of effective charge carrier density and their mobility in ion-conducting glass is still not fully understood. Performing independent measurements to separate this contribution is experimentally challenging mainly due to the low mobility of the ions. Electrochemical impedance spectroscopy (EIS) can be a powerful tool to solve this problem. In fact, the capacitance of the electrode polarization (measurable by EIS) is proportional to the number of mobile charge carriers. As a result, by knowing the ion species and its charge, one can determine the density of mobile ions involved in the ionic conduction and then calculate their mobility. However, there is a lack of information on how experimental factors, such as AC input voltage, sample roughness and thickness, affect the measured capacitance of the electrode. This work investigates the influence of these factors on the interfacial polarization of a gold electrode in lithium and sodium silicate glass. Thus, an optimized experimental condition was employed based on the evidence that the estimated effective charge carrier density is not significantly affected by surface roughness, while AC input voltage is important to prevent electrochemical processes and the thickness of the sample is relevant to ease the polarization process. The frequency range in which the polarization is revealed changes with temperature; therefore, a method is proposed to determine the ideal frequencies for the measurements. Our findings suggest that around 1 to 10% of all ions are mobile and thus contribute to the conduction process.
Acknowledgments: grant n° 2013/07793-6, 2021/12412-8 and 2021/06509-9, São Paulo Research Foundation (FAPESP). CAPES finance Code 001.